In a gear hobbing machine which is a hob, mounted on a spindle journalled in a hob slide cuts a gear blank mounted on a spindle which is carried by a work slide, the hob and gear blank are rotated in synchronism and, in each hobbing cycle, the hob and the gear blank approach one another prior to traverse of the hob past the work gear or vice versa and then are separated again.
The axis of the hob may extend vertically and the axis of the gear blank horizontally, or vice versa, or the two axes may both be horizontal and either the work slide or the hob may be advanced and retracted. In a typical case the axis of the hob is horizontal and that of the gear blank is vertical and the work slide is advanced towards the hob during each hobbing cycle, the hob then moving vertically to hob the gear blank, after which the work slide is then retracted and the hob is returned to its starting position.
During cutting only part of the length of the hob is engaged with the gear blank, and it is accordingly desirable to impart a short axial movement to the hob after each hobbing cycle so as to distribute the wear on the hob more evenly and thus increase its working life.
The object of the invention is to provide an improved and simplified form of hob shifting mechanism.